


At A Cost

by orphan_account



Category: Undertale (Video Game)
Genre: M/M
Language: English
Status: Completed
Published: 2016-04-19
Updated: 2016-04-19
Packaged: 2018-06-03 06:12:30
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,824
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6599914
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: <blockquote class="userstuff">
              <p>Alphys found a way to save Gaster from his dreaded fate, but he's not the same... (Warning: Dubcon)</p>
            </blockquote>





	At A Cost

"Are you sure about this?"

Alphys had lost track of the amount of times she'd asked the question. Her sweaty palms were clamped together hard, the pressure hurting her hands.  
He wasn't even supposed to find out about this. In fact, she hadn't even done it on purpose. Finding out that somehow, he'd survived, was enough to send her into a craze. She'd closed the doors to her lab, and shut out the whole world. No explanation, no warning, no nothing.

And from there, she worked. Doing everything in her power to find a way to save him. It took months, and she'd almost given up. Her mental health took a tumble, she barely ate, didn't shower.

Finally, she tested her methods. She shut down the power to the core, and left the lab, moving as fast as she could to reach it before Asgore realized what had happened.

On the way, she passed a crowd of monsters. They were huddled together, some of them crying, some of them angry. They were scared and confused at the sudden darkness that had taken over. Alphys winced as she passed, trying to block out their crying. Guilt crept up her back, but she forced it aside, as the amount of panicking would quickly alert the king. She had less time than she thought.

Her theory had been correct, but the quest itself nearly killed her. The darkness woke him, and he was angry and unstable. She realized far too late that it was safer for him to remain trapped.  
It was like he was everywhere, invading her mind. Deafening screams rang through her head. She couldn't breathe, couldn't think, couldn't move.

Then the room filled with the bright light of fire magic He shied away, attempting to flee, only to be trapped by a cage of flames. He thrashed wildly against it, burning himself and filling the room with a horrible smell. 

Asgore stood in the doorway, eyes wild. He would have yelled at Alphys if she didn't look like she could turn into dust any moment. Instead, he just stared in disbelief.

It became apparent very quickly that he was too unstable to live among monsters again, so Alphys took him back to the true lab, keeping him hidden in a high-security vault.  
And that's why the question burned in her mind:

How did Sans find out?

The skeleton looked certain, but scared as he stared at the doors in front of him. She almost thought he'd missed the question, and opened her mouth to ask again when he cut her off with a chuckle.  
"I'm sure, Alphys. I know the risks." he said. The scientist frowned, claws hovering over the number pad to open the final set of doors.  
"And you understand that if he attacks you...I can't...I won't b-be able t-to...what I'm saying is that i-if the need arises...you'll have to-"  
"Don't say it. I know." he interrupted, the small white lights vanishing from his eye sockets as he spoke. Alphys gulped, bringing her shaking hand down to the pad and tapping in the code. The doors started to peel open slowly.

Gaster was unmoving, in the far corner of the room. The only proof of him still being there was a mound of black goop. Sans was frozen in place for a moment, eyes locked onto the dark figure in the room. In a daze, he stepped into the room slowly.  
"Good luck." Alphys whispered, locking the door again quickly, shutting the skeleton in with the man who came from the other world.

Sans felt like he was in a trance. The last time he'd seen Gaster, he'd been a tall figure of authority, lab coat always stained, hard working and imposing. The figure before him was a stranger, in both body and soul.  
He tugged at the collar of his shirt, sucking in a deep breath.  
"Hey G...you remember me?" he asked cautiously. The mound in the corner shuffled slightly, and Sans froze again. He could see the edges of Gaster's face, and a glowing eye burned into him. He felt sweat break out on his bones.  
"G...buddy...it's Sans. Your old partner...ringing any bells?" he pressed, clenching his fists nervously. Gaster turned more, his whole face coming into view. Sans took a step back as he felt the weight of his intense stare weighing him down. A distorted noise rang through the room. It almost sounded like laughter. Gaster turned fully, his height stretching up, eyes wild. Hands appeared at his sides, making different motions rapidly. Sans stumbled back, tripping as a hand grabbed his ankle, dragging him closer to Gaster with a furious tug.

Suddenly, Sans was directly in the face of the man who spoke in hands. He had an unreadable expression, and it shook the skeleton to his core. Another distorted noise filled the room, loud, echoing, and angry. Sans couldn't understand a word, and barely had time to try to decipher it, before a hand swiped across his face, leaving a sting. The same hand then grabbed his face roughly, forcing Sans to look into Gaster's crazed eyes. Hands started grasping at parts of the short skeleton's body, restraining his arms and legs. Sans became aware of something wet slithering against his shirt, pulling the fabric back and then wriggling against his rib cage and spine.

"H-hey, what are...don't make me hurt you." he warned, his eye glowing for an extra effect to his statement. It didn't work, and Gaster rolled his eyes. More noises filled the room, but Sans could make them out this time.

"Y̝̞͎̱͇̭̟O͓̱U͈̭̗̭͈ ̙͕W̗̳͓͈O̺͙͓̳Ṇ͉̠̰̩͍'͎̮̣̘̣͈T̥͎̪̼̝͙.̬̠̙.̳.̬̟͉ ̣̖̦̺͕̺̼JU͍͓̠̰͍̱̫S̳T͔ ̘̻̣̟̳͚̺LO̻̭͖ͅO͚͙̩K̮̻̣ ̱̞͎͚̟A̹̪͙T͉ ̬̼̗Y̬O͚U̠̠R̫S̩̫̣̭Ḛ͉ͅḼ̙͈̼̜̝͖F.̜̜̙̣͙.̮̖̪̹.̜̱͖̼̩͎Y̭͍͈̮̙̻O̲͉͈͙̘̗U̮̱̗ ̫̹̹̹̳̣ͅL̳̥O̺̺̼V̜̥̖̩̫̪ͅE̙̘̩̰̹ ͓I͔̜̮͇T̲̹̘̤̣͙̜.̟̟͉̤͕͖.̮̹̠.͖͈̤̳̼͔ͅ. "

The wet limb beneath his shirt suddenly shot up, curling around the skeleton's soul, massaging it roughly. Sans let out a surprised gasp as he felt the pressure on his soul. The sensation was strange, but in the best way, sending shock waves through his body. His thoughts were ruled by the fact that he was now in a very dangerous position. One jolt and his soul could be snapped into a thousand pieces. He kept that thought in mind, but his body was slipping. He felt his bones buzzing with magic and didn't need to look to know why.

His mouth fell open as he started to pant, a blue tongue lolling from his mouth, dripping with saliva. Gaster's face twisted into a smirk, and soon Sans was staring at another tentacle. He barely had a moment to register it before it shot forwards into his mouth. The skeleton let out a muffled cry, and Gaster's eyes sparkled at the sound. Two more tentacles latched to Sans's body, roughly pulling down his shorts. Gaster paused, looking down at the source of the glowing blue light that had just started shining. His face twisted again, this time into a devilish grin. A tentacle wrapped around the length of Sans's member, slowly sliding up and down the length. Sans's eyes went wide at the feeling, then slammed shut as his moans were muffled by the tentacle in his mouth. It slowly slid out, and Sans opened an eye in confusion. Gaster's mouth opened, and a long, dripping, black tongue slipped out, licking up along the cheekbones of the shorter skeleton. He then dipped his head, forcing his tongue into Sans's mouth as he yanked his head towards him. The tentacle around his cock sped up drastically, and was joined by a smaller one that started teasing the tip, swirling around the top at a moderate pace.

It didn't take long to bring Sans to the edge, with Gaster's tongue swirling around his own, tentacles writhing along every place they could reach. He finally couldn't take it any more, bucking his hips frantically. Soon after, a scream tore from his throat, muffled by Gaster's mouth. The tentacles didn't slow, in fact they sped up. Sans's eyes opened, locking gazes with Gaster, who pulled his head back for a moment, ignoring the thread of black and blue saliva he left dripping onto Sans's hoodie. A much louder laugh echoed through the room.

"DI͇͔̜D ̩̻͎͙̠Y̪͖̳̻̖̮O̻̲U̝̩̯̫͖ ̤̘͉̬R̮̗͔E̩̥̟̼A̙̱͇̪̙L͔̹L̻̩̮̘̟Y̮̦ ͎͔T̥͓̺͙̠͓̼H̭̜̜ͅI͇̼N̞̤͎̠͕̗K̦͉̻͔̻ ͔͖̗I̪̣̬̠̞̙T W̰̯͈AS ̜̪̠O̘̝ͅV̬̤̱ͅͅE̳̳̦͉R̺̫̜?͔̳̠!̬̮͓" Gaster growled, lowering his head above Sans's neck and licking along the bones. The short skeleton winced, desperately gasping for air.

"P-please, G...I need to rest...a-ah!" he pleaded, over-stimulation crawling over him, giving him a numbing pain in his body. Gaster let out a cruel laugh, tightening the hold on Sans's dripping soul.  
"R̬͔̬̰̺E̩̩͖͈̘͈͇ṢT̤̤?̱͇͇̲̩̻ Y̱̣͙O͇͓̲̻U͇̪̼͔ ͙W̩̘̼͎̮̘͔I̞͉S͍̠̫͔̟͕H̯̮.͉͕̫͍͎.͍̠̮̪̙̥ͅ.͕" he sneered, squeezing Sans so tight he thought he would break.

"Y̤͈̠O̥̹̰͍̞U̼͈͓'R̼̘̞͇E͓̜̹̲̙̮͇ ̩̰͓̗̜ͅM̤̪̠̥̲I̳̲N̮̩̫̼͕̻͍E̠̗̩̗͎ ̳̟͚̬N̬̘̞̳̥̟O̳̲̜͕͚̞̥W̜̰̦.̖̳͓̜̖͙͇.̼̱.͍̩̯̱̗̩"

In the meantime, Alphys had fled the moment Gaster had attacked. She didn't want to know what he would do to Sans, and was sitting on one of the beds, clutching a pillow, rocking back and forth and shaking. Frightened tears slipped down her face as her mind raced about what to do. How to tell Papyrus. It was too much for her to handle. She passed out.

When she woke, the lab was far too quiet for her liking. She shot up like a bullet, sprinting down to Gaster's cell in the desperate hope that Sans was okay. She was terrified as she tried to tap in the code to open the door, getting it wrong twice before finally punching in the right code. The doors opened slowly, and when they did, Alphys was greeted by Gaster staring her down. Directly in front of her.  
She squealed as he grabbed her, bringing her up to his face. His eyes burned with a hungry expression, and his mouth was curled into a snarl.

"D̫̪͎̖͚̙ͅO̲̳̬̪͔̖ ̣̠N̟͎̘͙̠̣̦O̺T̝̣͖̫̯͍ ̜̹͈̭̠̹C̖̖̰OM̦ͅE̦̖ ̺̱̝̖͙B̝A͇CK̺̦̫̝͍̘ F̺̹O͈͔̳̞R̤̖ ̠͔̩͕̬H̠̪I̬̜̙M. ̗ͅH̯̯͇̜E̟͓̥̖̯ͅ ͙I̤̯̙̲̗̼S̳̝̬͖͚̹ͅ ̞͚̜M̠͚̱̭͖̘I̲͉̣͍̝͖N̳̹̙͔̙E̯̗.͈̤̮" he informed her, shoving a hand around her throat.

"D̹͇̥̰͕̺O̝̗ ̺̳͔̞̞YO͇̥̞͙U͕̝̭̦͇ ̦̤̹̝U͙͉N͍̝͔̭D͖̥̮E͔R̟͚̰̭͈S̳TA̳̝̗N̙̖̺ͅͅD̠̬͚͉?͖͕̦͙̙͚͇!̻̜̮̙̱̥"

Alphys nodded hastily, and Gaster let go of her, dropping her to the ground with a thud. She gasped for air, a hand racing to her throat. Behind Gaster, she could see Sans slumped against the far wall, his tongue hanging out, his clothes shredded, fragments strewn across the room. He was drenched in a strange black ooze. The scientist's eyes widened in shock, but the moment she tried to reach to the skeleton, Gaster summoned a plethora of hands that surrounded her, threatening to attack at the next wrong move. She squeaked, scrambling to her feet and running out of the room, tripping and falling onto her face once she was clear of the doorway.  
She stood slowly, dusting herself off and fearfully glancing back at Gaster. He had turned away from her.

She quickly hit the switch to close the door again. As the doors started to seal, Gaster's voice rung out dangerously, an order rolling off his tongue and echoing through the entire lab.

"B̝͍̱̊̆ͤ͂R͎͍͍ͤ͒̽̇͐I̟̜̟͉̝͚̭ͤ̐̅̂̚N̺̞̘͈ͩG̣̭ ̫̗̱̭M̯̎E͚̰ͬ͒͛̚ͅ ̼͉͕͉͈́̃ͮͩ̆H̯͕͇̣ͦI͉͙̋̒̐͌̐S̤̞̱̗̜̣̣ͭͭ̅̔̎ ̟̱̼̱͈ͅB̺͕̼̥͉̯̦̀̋̃̎ͣR͎̹͙̠͈͈̞̓̐̒̓̊Ō̮͈̭̱̳̩̰ͮTͤ͒́HͣE̲ͬ͐̂̾ͯR̘̗̺̭͎͂͋̓̔̚"

**Author's Note:**

> Well. What a way to start my AO3 account.
> 
> Please be kind, I still kind of have writers block.


End file.
